1. Field of the Invention
This invention relates to a photometric apparatus for detecting the brightness of an image based on an image signal from an endoscope imaging apparatus.
2. Related Art Statement
Recently, a video camera apparatus such as an electronic endoscope apparatus obtains an image signal using as an imaging means a solid state imaging device such as a CCD (charge coupled device).
FIG. 15 is a formation diagram of an example of the above mentioned electronic endoscope apparatus. An electronic endoscope apparatus 1 comprises an electronic scope 2 formed to be elongate so as to be inserted, for example, into a body cavity. A body unit 3 is connected to a universal cord (not illustrated) of the above mentioned scope 2. A monitor 4 displays an object to be photographed such as a body cavity interior part 5 from an output signal of the body unit 3.
A light guide 6, transmitting an illuminating light, is inserted through the insertable part of the above mentioned electronic scope 2 so that the illuminating light fed to the entrance end from the body unit 3 may be transmitted to the exit end and may be radiated toward the body cavity interior part 5. The light reflected from the body cavity interior part 5 is condensed by an objective lens 7, enters an imaging device 8 and is photoelectrically converted to be an image signal which is input to the body unit 3.
The above mentioned electronic scope 2 has a channel 9 through which a treating instrument 10 can be inserted into the body cavity. There are many treating instruments 10 which may be used such as a treating instrument having a function of injecting a coloring agent or image forming agent and a treating instrument having a function of taking out a part of tissues within a body cavity. Most of the treating instruments are made of white Teflon and metal.
The above mentioned body unit 3 comprises a light source part 20 illuminating an object to be imaged and an image signal processing part 30 outputting a video signal to a monitor 4. The above mentioned light source part 20 comprises a lamp 21, an iris 22 adjusting the light amount of the illuminating light of the lamp 21, an iris controlling circuit 23 generating a control signal for variably controlling the opening rate of the iris 22 and a photometric circuit 24 measuring the illuminating intensity of the light entering the imaging device 8 from the image signal and generating a signal to the iris controlling circuit 23. The above mentioned image signal processing part 30 comprises an AGC circuit 31 amplifying the image signal to a proper level, a photometric circuit 33 measuring the illuminating intensity of the illuminating light entering the imaging device 8 from the image signal and generating a signal to the AGC circuit 31 and a signal processing circuit 32 for variously processing the signal and outputting it to the monitor 4.
The above mentioned photometric circuits 24 and 33 are largely divided into an average photometric circuit and a peak photometric circuit. The above mentioned average photometric circuit is a circuit detecting the average value of the image signal levels of the entire picture and generating a signal so that, in case the average value of the image signal levels is high, the opening of the above mentioned iris 22 may be narrowed and the light amount of the illuminating light radiated toward the body cavity interior part 5 may be reduced. The above mentioned peak photometric circuit is a circuit detecting the maximum value of the image signal levels and generating a signal so that, in case the maximum value of the image signal levels is high, the opening of the above mentioned iris 22 may be narrowed and the light amount of the illuminating light radiated toward the body cavity interior part 5 may be reduced.
The above mentioned AGC circuit 31 is a circuit amplifying to a proper level the low image signal level which can not be compensated even by making the light amount of the illuminating light a maximum by expanding the opening of the above mentioned iris 22 to a maximum.
When the above mentioned electronic scope 2 is inserted into a body cavity and the treating instrument 10 is inserted through the channel 9, an image such as is shown in an example in FIG. 16 will be able to be observed in the monitor 4. FIG. 17 illustrates image signal levels by a time series of horizontal positions by noting a horizontal scanning line A--A' of the image shown in FIG. 16. The treating instrument 10 projects in a position nearer to the imaging device 8 than to the body cavity interior part 5. As white Teflon or the like is used, the illuminating light will be reflected at a high efficiency. As illustrated in FIG. 17, the image signal level Vs will become much higher than the average value Va of the image signal levels of the body cavity part 5. Therefore, in the photometric circuits 24 and 33, the average value will become high in the average photometric circuit and the maximum value will become high in the peak photometric circuit. Therefore, the signals generated by the photometric circuits 24 and 33 will not be of proper values, the light amount for the body cavity interior part 5 will be reduced and the amplifying degree of the AGC circuit 31 will also be reduced. Therefore, the image in the monitor 4 will become dark as a whole.
A prior art of reducing the influence on the object imaging of the level variation of the image signal in a specific part in an imaged picture is disclosed, for example, in a Japanese patent application laid open No. 110369/1987.
However, the above mentioned prior art example is effective only to object higher in the luminance in a peripheral part of the imaged picture than in the central part of the picture but is not effective for an object of high luminance over the range from a peripheral part to the central part of the picture by the treating instrument or the like, for example, in an electronic endoscope apparatus.